Irradiating system including a target-holder mounting in a radiation-protection enclosure and a device for deflecting an irradiation beam

ABSTRACT

Disclosed is a system for irradiating a target. The system includes a particle accelerator configured to at least emit an irradiation beam along an axis, a target-holder mounting outside the accelerator, a radiation-protection enclosure surrounding the target-holder mounting, and a deflection device. The particle accelerator is positioned outside the enclosure. The target-holder mounting includes at least one port configured to receive a target holder for a target to be irradiated. The target-holder mounting is stationary relative to the particle accelerator. The port is offset relative to the axis of the irradiation beam. The deflection device is positioned in the radiation-protection enclosure and is configured to divert the irradiation beam towards the port of the target holder in which the target to be irradiated is inserted.

BACKGROUND OF THE INVENTION Field of the Invention

The present application concerns a target irradiation system, and inparticular an irradiation system comprising a particle accelerator.

Description of the Related Art

Particle accelerators are pieces of equipment the object of which is toproduce beams characterized firstly by the nature of the particles(protons, electrons, etc.), the energy of the particles and the beamcurrent. According to the application for which the accelerator is used(production of radio-isotopes, radiotherapy by x-rays or gamma rays,production of neutrons, etc.) the beam may interact with different typesof target, for example principally:

Targets in the core of which nuclear reactions take place, for examplesuch as the targets used with cyclotrons for the production ofradioisotopes for Positron Emission Tomography (PET);

Stopping block targets the object of which is to stop and characterizethe beam at the time of the adjustment phases of the accelerator.

The interaction between the beam and the target may give rise todifferent types of reaction and therefore to different types ofradiation from the target.

As a matter of fact, an irradiated target in turn typically emitsradiation comprising in particular neutrons and photons at high energy,typically in the form of x-rays or gamma rays. These neutrons andphotons are said to be “primary” when they are produced directly by thenuclear reaction which takes place in the target and “secondary” whenthey arise from the reactions between the primary photons and neutronsand the surrounding matter.

A cyclotron is a particle accelerator frequently used in medical imagingfor the production of radioactive isotopes with a very short half-life,or even of a half-life equal to or less than two hours for example suchas the following elements: ¹⁸F (fluorine 18): 109.7 minutes, ⁶⁸Ga(gallium 68): 67.7 minutes. ¹¹C (carbon 11): 20.4 minutes. Other typesof particle accelerators may of course be envisioned for example such asa linear accelerator (LINAC) or a synchrocyclotron.

For example, a cyclotron producing a proton (p) beam at 2 MeV and 20 μA(microamperes) interacting with a target comprising water enriched with¹⁸O (oxygen 18) to 95% produces ¹⁸F (fluorine 18) accompanied by a fluxof neutrons (n) and photons in a certain proportion, for exampletypically 6*10¹¹ G/s (gamma per second) and 4*10¹¹ n/s (neutrons persecond). This reaction is for example notated: ¹⁸O→¹⁸F+n.

According to another example, the interaction between the same beam ofprotons (p) but this time with a target comprising ¹⁴N (nitrogen 14)will produce ¹¹C (carbon 11) and high energy neutrons and photons, butin different proportions to those of the preceding reaction, for exampletypically 1*10¹² G/s and 2*10⁹ n/s at 20 μA.

The cumulative dose rate near the targets is thus considerable (severalSv (Sievert, with 1 Sv=1 m².s⁻²=1 J.kg⁻¹) per second in contact with atarget for producing ¹⁸F and a beam of 20 μA protons at 12 MeV(megaelectronvolt)). These intense radiations are ionizing and thusdangerous for humans and the environment. The intensity of theseradiations is approximately a million times greater than that of theradiation emitted by a cyclotron with an external source of ionsproducing the beam described above, that is to say with 20 μA protons at12 MeV. In the case of a cyclotron with an internal source of ions, theradiation emitted by the acceleration of the ions in the cyclotron isgreater, which reduces this ratio by the order of a million between theradiation intensities of a cyclotron and of a target, but the targetremains the main radiation source.

In the example cited above, the energy spectrum of the particles emittedby the accelerator possesses a maximum located on average around 2 MeV;there are thus particles which can be emitted at higher energies. Theradiation from the targets may in turn interact with items in thesurroundings (air, equipment, walls, etc.) and activate those items.Depending on the materials used for the target holder, radioactiveisotopes with a half-life that is short or even long (that is to saywith a half-life of at least 100 days, or even a few years) may becreated, which represents a drawback for this type of technology.

It is thus important to protect persons and the surroundings from theionizing radiation to limit the risks of irradiation and activation ofthe items of the surroundings in operation of the accelerator. Inparticular, persons and the surroundings should be protected from theradiation from the target.

In order to protect persons and the surroundings from this ionizingradiation, such systems are often installed in hot cells that are heavy,bulky and expensive. As a matter of fact, the walls of a hot cell aregenerally very thick: of the order of 2 meters thickness of concrete.

However, it is not always possible to construct a hot cell in existinginstallations, such as in a hospital department for example.

The development of certain applications is therefore hindered byconstraints associated with the possibilities of installing theseirradiation systems.

To reduce this bulk, particle accelerators are sometimes equipped with achamber for radio protection referred to as “local”. This makes itpossible to reduce the flux of radiation in the hot cell but not todispense with a hot cell.

By way of example for such radiation protection, in order to attenuateat least the primary and/or secondary high energy photons coming fromthe target, it is for example worthwhile to use so-called “dense”materials. Concrete and lead are often used as “dense” materials inparticular for reasons of cost and ease of implementation. However, inthe interest of compactness and mass reduction, it may be advantageousto use materials that are still more dense, for example such astungsten.

The attenuation of neutrons is possibly carried out in two steps, i.e.for example, in a first phase, slowing the neutrons, then, in a secondphase, trapping the neutrons. The neutrons are for example slowed byelastic impacts with material. Hydrogenated compounds (water, certainpolymers, etc.) are for example well-adapted to slow the neutrons. Oncethe neutrons have been slowed, they are for example trapped by a“neutron trap” or “neutron poison”. Boron may for example be used tocapture the neutrons. One solution consists for example of adding a fewpercent of boron, typically 1% to 8% (atomic) as a filler to ahydrogen-rich material, for example such as polyethylene. In the contextof the present application, “rich” means that the amount of hydrogen isequal to or greater than approximately 30% or even 40% atomicconcentration in the filled material.

However, the capture of neutrons in turn generates so-called “secondary”high energy photons which must in turn be attenuated.

Thus, to attenuate these different radiations, a radiation protectionchamber for a target such as a target for producing ¹⁸F comprises forexample a succession of layers of material rich in hydrogen comprising aneutron poison and layers of dense material.

In order to attenuate both primary and secondary high energy photons andneutrons, these functions may possibly be combined, for example byadding boron and a dense material such as lead or tungsten, as fillersto a resin.

Furthermore, as the targets are generally positioned in the immediatevicinity of the acceleration zone, or are even mounted directly at theoutlet from the particle accelerator used, the radiation protectionchamber thus encompasses both the target and the particle accelerator.

It follows that such a radiation protection chamber does not thereforeprevent the radiation coming from the target from significantlyactivating the particle accelerator and that the mass of the radiationprotection remains high (typically 40 to 80 metric tons for cyclotronsproducing protons of 10 to 18 MeV, to which 10 to 20 metric tons are tobe added for the particle accelerator itself).

These solutions thus make it possible to reduce the risks associatedwith the non-remnant radiation but do not protect the accelerator fromactivation by the radiation coming from the target and, on account oftheir mass, do not facilitate the installation of the accelerators, orare sometimes even prohibitive for an installation in pre-existingbuildings.

To avoid the activation of the particle accelerator by the target, onepossibility lies in the fact of offsetting the target at a distance fromthe accelerator, which thereby makes it possible to dispense withencompassing the particle accelerator within the radiation protectionchamber and thereby limit the radiation to as close as possible to thetarget.

The activation of the accelerator is then much lower when the target isoffset and radiation protected than when the target is mounted directlyon the accelerator and the assembly is radiation protected.

This also makes it possible to considerably reduce the size, andtherefore the mass, of the radiation protection chamber since it maythen no longer contain the particle accelerator.

On the other hand, it is still possible for the radiation to follow theirradiation beam emitted by the particle accelerator and activate theinterior of the accelerator. This is particularly a hindrance forneutron that “rebound” against the metal surfaces of the accelerator byelastic impact. If the installation constraints cause the constructionof thick walls to be avoided, this sending back of neutrons is all themore a hindrance in that it generates a high dose rate by itself.

The use of an offset target thus makes it possible to greatly reduce theradiation protection mass, but risks of irradiating the surroundingslinked to such neutron leakage remain.

Furthermore, for certain applications, it may be advantageous to be ableto use different targets with a same accelerator.

One solution that may be envisioned is then to move the selected targetto face the irradiation beam.

However such a solution generally requires destroying a pre-existingvacuum in the system, changing the target then re-establishing thevacuum before being able to re-use the system.

Furthermore, in order for the irradiation of the target to be as optimalas possible, it is necessary for the target to be positioned facing thebeam as much as possible. The effect of this is to create a direct pathof leakage for the ionizing radiation (high energy photons and neutrons)from the target towards the cyclotron. This has two consequences. Thefirst is that part of the cyclotron is still capable of being activated.The second is that the neutrons which follow the line of the beam“rebound” by elastic impact on the metal parts of the cyclotron and thuscreate a secondary radiation source which must be shielded.

Document U.S. Pat. No. 5,608,224 describes for example a devicecomprising a barrel making it possible to use different targets.Although this solution may enable a change in target without destroyingthe vacuum, it is directed in parallel to ensuring that the target toirradiate is positioned as well as possible in line with the collimatorof the irradiation beam. Such a solution does not therefore enable theproblem of neutrons coming back towards the particle accelerator.

BRIEF SUMMARY OF THE INVENTION

The object of the present application is directed to solving theaforementioned drawbacks at least in part.

To that end, according to a first aspect, there is provided anirradiation system for irradiating a target, comprising at least:

-   -   a particle accelerator configured at least to emit an        irradiation beam along an axis,    -   a target holder mounting, positioned outside the accelerator        facing the irradiation beam, comprising at least one port        configured to receive a target holder configured to receive a        target to irradiate, and    -   a radiation protection chamber surrounding the target holder        mounting, the particle accelerator being positioned outside the        chamber,        the system being characterized in that the target holder        mounting is fixed relative to the particle accelerator and in        that the port is axially offset relative to the axis of the        irradiation beam, and in that the system comprises a deflection        device, positioned in the radiation protection chamber and        configured to deviate the irradiation beam towards the port of        the target holder in which the target to irradiate is inserted.

The solution provided here thus consists of using a beam deflectiondevice which enables the beam to be directed towards a target insertedinto a target holder mounted on a fixed port and positioned outside thesolid angle of leakage of the irradiation beam or making it possible toaddress one among multiple target holders pre-positioned on differentports. The deflection device thus serves as a target selector, or targetchanger by analogy.

Preferably, the target mounting comprises at least two ports, forexample five ports.

For example, at least one of the ports, or even all the ports, areaxially offset relative to the axis of the irradiation beam emitted bythe particle accelerator.

According to an example embodiment, the ports are disposed in a sameplane.

Furthermore for example, the plane in which the ports are disposed is ahorizontal plane.

According to an example embodiment, the ports are disposed within avolume.

It then becomes possible to attain different targets surrounded by aradiation protection while minimizing the leakage paths. Thus the doserate near the corresponding target holder and the particle acceleratorand the activation of the nearby equipment, that is to say the items inthe surroundings, are low while having a reduced protection mass.

The radioprotection chamber makes it possible to attenuate the remnantand non-remnant radiation generated by the interaction between thetarget and the beam and the combination between the use of a beamdeflection device and of a radioprotection chamber brought close aroundthe target holders makes it possible to reduce, or even eliminate, thedirect leakage paths of radiation from the targets towards the particleaccelerator while making it possible to reduce the radioprotection mass,possibly by a factor of 5 to 15, while maintaining effective radiationprotection.

For example, the radiation protection chamber comprises an alternatingarrangement of at least one layer comprising a dense material and atleast one layer comprising a hydrogen-rich material comprising a neutronpoison.

For example, the hydrogen-rich material is polyethylene (PE) with aboron filler as neutron poison in an amount of approximately 5% to 7%(atomic).

For example, the dense material is tungsten (W) and/or lead (Pb).

Optionally, the radiation protection chamber further comprises anadditional radiation protection part which surrounds the target holdersmounted on the target holder mounting. The additional part is forexample positioned within a wall of the radiation protection chamber.Such a part is for example fastened on the target holder mounting.

Preferably, with the radiation protection layer positioned closest tothe target holders, the additional part if present, is of densematerial.

In other words, a layer of radiation protection of the radiationprotection chamber near an inside surface of the chamber is a layer ofdense material.

In an example embodiment, the radiation protection chamber comprises awall which comprises an additional thickness of hydrogen-rich materialpositioned between the radiation protection additional part of thetarget holders and the innermost layer of dense material.

In an example embodiment given by way of illustration, the radiationprotection additional part is of tungsten (W) and is of thicknesscomprised between approximately 5 cm and approximately 15 cm, forexample approximately 6 cm or 11 cm.

The wall of the radiation protection chamber next comprises for example:

-   -   The additional thickness of hydrogen-rich material of a        thickness comprised between approximately 5 cm and approximately        15 cm, and is of PE having 5% boron filler;    -   The innermost layer of dense material of a thickness comprised        between approximately 3 cm and approximately 8 cm, and is of        tungsten (W);    -   A next layer of hydrogen-rich material of a thickness comprised        between approximately 25 cm and approximately 40 cm, and is of        PE having 5% boron filler;    -   A following layer of dense material of a thickness comprised        between approximately 2 cm and approximately 8 cm, and is of        lead (Pb); and    -   An outermost layer of hydrogen-rich material of a thickness        comprised between approximately 15 cm and approximately 30 cm,        and is of PE having 5% boron filler.

Such a chamber then comprises four layers and an optional additionalthickness, in addition to a possible additional part.

The thickness values are of course given by way of indication in orderto evoke an order of magnitude and may vary by a few centimeters, forexample by +/−5 cm.

Such a chamber is particularly compact.

An order of magnitude of the thickness of the wall is thus comprisedbetween approximately 50 and approximately 100 cm, in particular betweenapproximately 60 cm and approximately 75 cm.

In a particularly advantageous example, the radiation protection chambercomprises at least one spherical wall.

Such a wall for example has an outside diameter at maximum equal toapproximately 3 m (meters), or even 2 m.

According to another example embodiment, the radiation protectionchamber comprises at least one wall with a parallelepiped geometry,which enables production costs to be reduced. At least one of its width,length or height dimensions is then possibly at maximum equal toapproximately 3 m (meters), or even 2 m.

Such a system thus makes it possible to reduce the risks of exposure toradiation and minimizes the constraints of masses and volumes for theinstallation of such a system, for example in a hospital environment.

It is however to be noted that there was a high prejudice on the part ofthe Person Skilled in the Art against the idea of being able to use sucha device.

As a matter of fact, in view of the usual energy ranges of theirradiation beam, the deflection device must also employ high energies.

This is all the more notable in that to be able to have a deviationmaking it possible to avoid as well as possible neutrons going backtowards the particle accelerator and to limit the mass of the assembly,it is preferable for the angle of deviation to be the greatest possiblerelative to the initial axis of the beam, for example at least 5°, oreven 10°, for example, comprised between 5° and 175° or between 5° and40°, and in particular for example between approximately 19° andapproximately 38°. Therefore, it is preferable for the deflection deviceto be positioned closest to the target holder mounting, or even at theentry to the target holder mounting.

Thus, in other words, the deflection device is then advantageouslyconfigured to deviate the beam, relative to the axis on which it isemitted by the particle accelerator, through an angle of at least 5°, oreven 10°, for example comprised between 5° and 175°, for example between5° and 40°, and preferably between 19° and 38°.

For this, it is for example configured to emit a magnetic field. Forexample, the magnetic field has a value between 1 and 2 Tesla (T).According to a particular example, the magnetic field is of the order of1.4 Tesla.

According to an advantageous example embodiment, the deflection devicecomprises at least one electromagnetic quadrupole positioned on a pathof the irradiation beam, that is to say typically on the axis ofemission of the beam by the particle accelerator. The electromagneticquadrupole comprises for example an electromagnet, or even fourelectromagnets.

According to preferred examples, the deflection device comprises asingle electromagnetic quadrupole, or else two electromagneticquadrupoles.

Instead of a quadrupole, there is preferably a dipole.

Other deflection devices may also be used according to the type and theenergy of the accelerated particles, for example such as anelectrostatic deflector for lighter particles (like electrons) and/or oflower energies.

The deflection device is also positioned in the radiation protectionchamber. It is to be noted that the deflection device also participatesin the radiation protection. For this, it is for example composed of adense material, for example of copper and/or of iron in particular,which makes it effective for attenuating photons. In the context of aquadrupole, this is for example an iron core surrounded by a copperwire, for example an iron yoke and a copper winding.

This raised an additional prejudice against the exploration of such asolution since such a deflection device then preferably being positionedwithin the protection chamber, another difficulty could lie in thechoice of the configuration of the passage of the supplies necessary forthe operation of the deflection device through the protection chamber.

According to an advantageous example embodiment, the passages for thesupplies, for example cables or pipes, are chicaned.

Once these prejudices have been overcome, by virtue of such positioning,the deflection device itself participates, in the radiation protectionby attenuating the high energy photons.

Furthermore, if the target holder mounting nevertheless comprises a portpositioned in alignment on the axis of the beam, the target of thetarget holder mounted on that port is preferably a target having asource term low in neutrons, that is to say of which the neutron flux isless than 100 smaller than the primary photon flux (for example hereapproximately 1*10¹⁰ n/s). This may for example be a charge target (thatis to say a target which makes it possible to adjust the cyclotronsuitable for being irradiated but which does not produce any radioactiveproducts), for example of graphite, for the adjustment, or even possiblya target for producing carbon 11 since the latter radiates relativelyfew neutrons for a beam such as described above, that is to say of 20 μAof protons at 12 MeV. Thus, it is preferable to mount the target holdercontaining the least used target and/or that having the lowest sourceterm (a charge target for example) on the port aligned on the axis ofthe beam.

Such a system furthermore has the advantage of being able to be morereactive than a system with a mechanical target changer. In other words,it is possible to pass the beam from one target to another positioned intwo target holders mounted on two different ports more rapidly than witha usual mechanical system and without destroying the vacuum, typicallywithin one second.

According to an advantageous example embodiment, the system comprises adevice for adjusting the position of the irradiation beam and a devicefor adjusting the focus of the irradiation beam, and the positionadjusting device and the focus adjusting device are positioned upstreamof the deflection device.

In an example embodiment, the deflection device differs from theposition adjusting device.

In an example embodiment, the position adjusting device and the focusadjusting device are positioned outside the radiation protectionchamber.

In another example embodiment, the position adjusting device and thefocus adjusting device are positioned at least partly inside theradiation protection chamber, or even at least partly within the wall ofthe radiation protection chamber.

In an example embodiment, the position adjusting device and the focusadjusting device are for example conjointly produced by a pair ofelectromagnetic quadrupoles.

According to still another advantageous example embodiment, the systemcomprises an automatic module comprising a control module and a commandunit, the control unit being configured to integrate information andmeasurements concerning the position and the focus of the irradiationbeam and to send instructions to the command unit, and the command unitbeing configured to actuate the position adjusting device and/or thefocus adjusting device and/or the deflection device in order to optimizean interaction between the irradiation beam and the target to irradiate.

Another object of the invention is a target holder mounting, taken inconjunction with its radiation protection chamber, but without theaccelerator. More particularly, this other object is a target holderassembly having a reference direction in which it is adapted to besubjected to an irradiation beam, comprising:

a target holder mounting, adapted to be positioned facing opposite saiddirection, comprising at least one port configured to receive a targetholder configured to receive a target to irradiate, and

a radiation protection chamber surrounding the target holder mountingand being passed through by said direction,

the assembly being characterized in that the target holder mounting isfixed relative to said direction and in that the port is axially offsetrelative to that direction, and in that the assembly comprises adeflection device, positioned in the radiation protection chamber andconfigured to deviate an irradiation beam received in said directiontowards the port of the target holder in which the target to irradiateis inserted.

Such an assembly is in particular configured for a system such asdefined above, comprising all or some of the features described above.

The direction may be materialized in the radiation protection chamber bya channel along which the radiation protection is reduced, or is even ofno significance, for example a hollow channel.

Such a system is thus particularly compact.

By virtue of such a system, it is thus possible to dispense withinstalling an entire wall between the particle accelerator and thetarget holders.

Such a system may thus be installed in the room of a building, forexample a room of a hospital or research complex, while making itpossible to avoid requiring notable architectural adaptation ortransformation, that is to say in a room with walls of ordinaryconstruction materials (such as concrete and/or metal reinforcements,etc.).

For example, walls of 40 cm of concrete suffice whereas it was necessaryto have 2 m for devices of the prior art.

Such a system, and in particular the radiation protection chamber, isthus independent from the room in which it is then installed.

In other words, such a system is thus configured to be installed in aroom of a building.

Another way to define the system is to state that it is disposed in aroom, or even in a chamber, which surrounds the entire system, thetarget holders are then disposed within an additional chamber, theaforementioned radiation protection chamber, such that the system isisolated from an external environment and the target holders areisolated not only from the external environment but also in relation tothe particle accelerator which, in such a system, is less activated incomparison with the devices of the prior art. The system thus presents adegree of autonomy.

As it is therefore possible for the system to be installed in a singleroom, all access to the system is thus facilitated. The system canfurthermore be installed more easily.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, according to an example embodiment, will be wellunderstood and its advantages will be clearer on reading the followingdetailed description, given by way of illustrative example that is in noway limiting, with reference to the accompanying drawings in which.

FIG. 1 diagrammatically illustrates a system for irradiating a targetaccording to an example embodiment of the present invention,

FIG. 2, composed of FIGS. 2a and 2b , diagrammatically illustratesexamples of geometrical arrangements of the position of the ports.

FIG. 3 presents by way of indication a change in the mass M (in metrictons, T) of a radiation protection chamber according to its insideradius Ri (in millimeters, mm), and

FIG. 4 represents a synoptic diagram of driving a position adjustingdevice and a focus adjusting device by a control module.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Identical parts represented in the aforementioned figures are identifiedby identical numerical references.

FIG. 1 presents an irradiation system 1 comprising a particleaccelerator 10, a target holder mounting 20 and a radiation protectionchamber 30.

The particle accelerator 10 is for example a cyclotron. It is forexample configured to emit an irradiation beam 11 comprising a beam ofprotons of several megaelectrons (MeV).

The radiation protection chamber 30 here surrounds the target holdermounting 20. The particle accelerator 10 is positioned outside thechamber 30.

The radiation protection chamber 30 for example takes the form of ahollow sphere, comprising a wall formed by stacking successive layers.

For example, the wall of the radiation protection chamber 30 comprisesan alternating arrangement of a layer of a so-called “dense” material 31and of a layer hydrogen-rich material 32.

In practice, it is preferable for the radiation protection chamber tocomprise at least two layers, for example between two and ten layers,alternately forming a layer of dense material and a layer ofhydrogen-rich material.

In order to limit the mass and bulk of the radiation protection, it isfurthermore advantageous to position a layer of dense material 31closest to target holders 22 mounted on the target holder mounting 20,as described later, to firstly attenuate the primary rays.

It is next preferable to alternate layers of hydrogen rich material 32,advantageously comprising neutron poison, with layers of dense material31 which attenuate the last primary rays as well as the secondary raysarising from the neutron capture.

By way of illustration, in the present example embodiment of FIG. 1,starting from the outermost layer, the wall comprises four layersalternating hydrogen-rich material 32 and dense material 31 such thatthe innermost layer, that is to say situated closest to the targetholders 22 is a layer of dense material 31.

Furthermore here, to reinforce the radiation protection, the targetholders 22 mounted on the ports 21 of the target holder mounting 20 aresurrounded by a radiation protection additional part 33 which ispreferably of dense material. The radiation protection chamber wall thencomprises an additional thickness 34 of hydrogen-rich materialpositioned between the radiation protection additional part 33 of thetarget holders and the innermost layer of dense material 31.

The hydrogen-rich material 32 is for example polyethylene (PE),optionally with a boron filler as neutron poison in an amount ofapproximately 5% to 7% (atomic). In the case of a cyclotron bombarding atarget for producing ¹⁸F at 20 μA, digital simulations have shown anoptimum attenuation if the PE has a filler of boron in an amount ofapproximately 7% (atomic).

The dense material 31, which mainly enables the primary and secondaryhigh energy photons to be attenuated, is advantageously of tungsten forexample. As tungsten is very dense, it enables a radiation protectionchamber to be produced that is more compact and light. As tungsten ishowever difficult to machine, it may be replaced by other materials suchas lead. As lead is less dense than tungsten, replacing the tungstenwith lead however slightly increases the diameter of the radiationprotection chamber and therefore its mass.

In a preferred example embodiment, the radiation protection additionalpart 33 is of tungsten (W) and has a thickness of approximately 6 cm.The wall of the radiation protection chamber 30 next comprises:

-   -   The additional thickness 34 of hydrogen-rich material has an        inside radius (Ri) of approximately 24 cm and an outside radius        (Re) of approximately 30 cm, i.e. a thickness of approximately 6        cm, and is of PE having 5% boron filler;    -   The innermost layer of dense material 31 has an inside radius        (Ri) of approximately 30 cm and an outside radius (Re) of        approximately 35.5 cm, i.e. a thickness of approximately 5.5 cm,        and is of tungsten (W);    -   The following layer of hydrogen-rich material 32 has an inside        radius (Ri) of approximately 35.5 cm and an outside radius (Re)        of approximately 64.5 cm, i.e. a thickness of approximately 29        cm, and is of PE having 5% boron filler;    -   The following layer of dense material 31 has an inside radius        (Ri) of approximately 64.5 cm and an outside radius (Re) of        approximately 68.5 cm, i.e. a thickness of approximately 4 cm,        and is of lead (Pb); and    -   The outermost layer of hydrogen-rich material 32 has an inside        radius (Ri) of approximately 68.5 cm and an outside radius (Re)        of approximately 88.5 cm, i.e. a thickness of approximately 20        cm, and is of PE having 5% boron filler.

By way of example, if the cyclotron and the target holder mountingdescribed here are used up to one hundred and sixty minutes per day and23 days per month, it is possible to produce a radiation protectionchamber of approximately 6.6 metric tons for an inside radius of 240 mm.Such a radiation protection chamber 30 thus makes it possible to reducethe dose rate outside the walls of 30 cm of ordinary concrete to lessthan 80 μSv/month, which is the limit set by the EURATOM directives forpublic areas.

The target holder mounting 20 is positioned facing the irradiation beam11, in the radiation protection chamber 30.

It comprises several ports 21 each configured to receive a target holder22, containing when the time comes a target to irradiate, which areaxially offset relative to the irradiation beam 11.

Here, in order to simplify the representation, the target holdermounting 20 comprises two ports 21 each with one target holder 22, whichare axially offset relative to the irradiation beam 11; as well as anadditional port 21′ positioned in alignment on the axis of the beam.

As FIG. 1 illustrates, according to the position of the port 21considered, this makes it possible to reduce to a greater or lesserextent the direct leakage paths 12 that are produced when a target,inserted in the target holder mounted on the port 21 considered, isirradiated by the irradiation beam 11.

When targets of different types are inserted into the ports 21 or 21′,it is preferable to position the targets generating the most intenseneutron flux in the ports 21 forming the greatest angle with theirradiation beam 11. A target generating less radiation and/or which isless used, such as a charge target, may be inserted in the port 21′ thatis aligned on the axis of the beam when there is such a port.

For example, starting from the axis of the beam and moving awaytherefrom, a possible configuration would be to position a charge targetin port 21′ situated in alignment on the axis of the beam 11, then atarget for producing ¹¹C then a target for producing ¹⁸F. These targetsare thus classified in increasing order of neutron flux generation at aconstant current.

It is to be noted that if a port 21 or 21′ is left vacant, that is tosay that no target is inserted therein, it is preferable to place anobturator therein, forming a fluid-tight plug, in order to better ensurethe sealing of the system.

The number of ports 21, or even the existence of a port 21′, depends onthe needs linked to the application considered.

In the context of applications of PET type, it is advantageous to beable to dispose of at least two target holders, in order to be able touse at least two different targets, for example between two and tentarget holders to be able for example to use up to ten differenttargets. It is thus useful to have as many ports are there are targetholders required.

According to the constraints of bulk that exist in the context of theapplication considered, the ports are for example arranged in a plane asillustrated in FIGS. 1 and 2 a or in three dimensions, that is to say ina volume, as illustrated in FIG. 2 b.

To address a target positioned in any one of the target holders of theports 21 based on the same irradiation beam 11, the system 1 furthercomprises an irradiation beam deflection device 40, configured toorientate the irradiation beam 11 towards each of the ports 21, forexample such that in operation, the protons bombard a target positionedin one of the target holders mounted on one of the ports 21 of thetarget holder mounting 20.

The deflection device 40 is also positioned in the radiation protectionchamber 30. It is to be noted that the deflection device 40 alsoparticipates in the radiation protection. For this, it is for examplecomposed of a dense material, for example of copper and/or of iron inparticular, which makes it effective for attenuating photons. In thecontext of a quadrupole, this is for example a core of iron surroundedby a copper wire.

The deflection device 40 comprises for example a deflector comprisingfor example a quadrupole formed from electromagnets, or preferably adipole. Such a deflector is then positioned on a path of the irradiationbeam 11 and is passed through by it, as FIG. 1 shows diagrammatically.Other deflection devices 40 may also be used according to the type andthe energy of the accelerated particles, for example such as anelectrostatic deflector for lighter particles (like electrons) and/or oflower energies.

In the case of a three-dimensional arrangement as in FIG. 2b , the beam11 must then be deviated in two dimensions (whereas a deviation only inone dimension is necessary in the context of the arrangement of FIG. 2a), which may imply that the deflection device 40 will be morevoluminous, inducing an increase in the internal volume of the radiationprotection chamber 30, and therefore a greater inside radius Ri of theradiation protection chamber 30, which then increases the mass M of theradiation protection chamber 30, as FIG. 3 illustrates, which may createadditional complexity.

The distance between a target holder of a port 21 and the ground at thelocation at which the system 1 is installed however limits the maximumpossible dimension of the radiation protection chamber 30. Thus, it isadvantageous to dispose the ports 21 in a horizontal rather thanvertical plane.

This furthermore makes it possible to limit the dose rate at the floorand thus more easily install the system 1 above the ground floor of abuilding for example.

In the present example embodiment, in the interest of compactness, thedistance separating the particle accelerator 10 from the target holdermounting 20 is for example very slightly greater than the distanceestablished between a port 21 and the ground.

In order to ensure correct focusing and correct positioning of theirradiation beam 11 at the location of the deflection device 40 and ofan entry window of each port 21, the system 1 here comprises anirradiation beam position adjusting device 51 and an irradiation beamfocus adjusting device 52.

The deflection device 40 differs from the position adjusting device, inparticular in that the deflection device 40 makes it possible to deviatethe irradiation beam through angles of at least 5°, whereas a positionadjusting device only makes it possible to adjust a position of thepoint of impact or focal point of the beam, that is to say over scarcelya few tenths of degrees, typically less than 0.5°.

In the present example embodiment, the position adjusting device and thefocus adjusting device are mounted upstream of the deflection device 40,it being understood that “upstream” refers here to a direction ofemission of the irradiation beam, from the accelerator towards thetarget holder mounting. They are furthermore both positioned hereoutside the radiation protection chamber 30; however, they could also bepositioned at least partly inside the radiation protection chamber, oreven at least partly within the wall.

The position adjusting device 51 and the focus adjusting device 52 arefor example conjointly formed by a pair of electromagnetic quadrupoles.However, if the beam diverges sufficiently little, that is to say bytypically of the order of less than 0.5°, it is not necessary to use afocus and/or position adjusting device.

To facilitate and increase the reliability of use of such a device, thedeflection device 40 is for example modifiable and drivable remotely inorder to address a target selected from the multiple targets that can beinserted into each of the target holders 22. In parallel, the positionadjusting device 51 and the focus adjusting device 52 of the irradiationbeam may also be rendered automatic to optimize the irradiation of thetarget considered.

For this, the system 1 for example comprises, as is the case here, anautomatic control module 60 comprising for example a control module 61and a command unit 62.

It is then possible to control the position adjusting device 51 and thefocus adjusting device 52 in order to perform the positioning in threedimensions of the focal point of the irradiation beam 11 relative to anentry window of the port 21 considered, or even of the port 21′.

A geometric measuring module 63, for example of Beam Position Indicator(BPI) type, is for example possibly used here to send information to thecontrol module 61 concerning the position and the dimensions of the beam11 at the location of the entry window of the port 21, or even 21′,containing the target to irradiate.

A module for measuring current 64 is for example also used to measurethe current generated by the beam 11 on the target and communicate thecurrent measurements to the control module 61.

This information and measurements enable the parameters to be adjustedof the devices for adjusting position 51 and focus 52 as well as of thedeflection device 40 such that the interaction between the beam 11 andthe target are optimal.

For this, the control module 61 integrates the information andmeasurements supplied by the module 63 and the measuring module 64 andsends instructions to the command unit 62 which actuates the positionadjusting device 51 and/or the focus adjusting device 52 and/or thedeflection device 40.

The invention claimed is:
 1. A target irradiation system, comprising: aparticle accelerator configured to emit an irradiation beam along anaxis; a target holder configured to receive a target that is to beirradiated; a target holder mounting that is positioned outside theparticle accelerator facing the irradiation beam and that is fixedrelative to the particle accelerator, the target holder mountingcomprising at least two ports axially offset relative to the axis of theirradiation beam, at least one port of the at least two ports beingconfigured to receive the target holder that is configured to receivethe target that is to be irradiated; a radiation protection enclosuresurrounding the target holder mounting, the particle accelerator beingpositioned outside the enclosure, the radiation protection enclosurecomprising an alternating arrangement of at least one layer comprising afirst material and at least one layer comprising a hydrogen-richmaterial comprising a neutron poison, the radiation protection enclosurehaving a wall thickness less than 100 cm; and a deflection device thatis positioned in the radiation protection enclosure and configured todeviate the irradiation beam towards the at least one port of the atleast two ports of the target holder mounting receiving the targetholder in which the target to be irradiated is inserted.
 2. The systemaccording to claim 1, wherein the first material is a layer of radiationprotection of the radiation protection enclosure near an inside surfaceof the enclosure.
 3. The system according to claim 1, wherein thehydrogen-rich material is polyethylene (PE) with a boron filler asneutron poison in an amount of approximately 5% to 7% (atomic).
 4. Thesystem according to claim 1, wherein the first material is tungstenand/or lead.
 5. The system according to claim 1, wherein the radiationprotection enclosure further comprises a radiation protection additionalpart which surrounds the target holder, within a wall of the radiationprotection enclosure.
 6. The system according to claim 5, wherein theradiation protection additional part is of the first material.
 7. Thesystem according to claim 5, wherein the radiation protection enclosurecomprises a wall which comprises an additional thickness ofhydrogen-rich material positioned between the radiation protectionadditional part and the innermost layer of the first material.
 8. Thesystem according to claim 7, wherein the radiation protection additionalpart is of tungsten (W) and is of a thickness comprised betweenapproximately 5 cm and approximately 15 cm, and wherein the wall of theradiation protection enclosure further comprises: the additionalthickness of hydrogen-rich material of a thickness comprised betweenapproximately 5 cm and approximately 15 cm, and being of PE having 5%boron filler, the innermost layer of the first material of a thicknesscomprised between approximately 3 cm and approximately 8 cm, and beingof tungsten (W), a next layer of hydrogen-rich material of a thicknesscomprised between approximately 25 cm and approximately 40 cm, and beingof PE having 5% boron filler, a following layer of the first material ofa thickness comprised between approximately 2 cm and approximately 8 cm,and being of lead (Pb), and an outermost layer of hydrogen-rich materialof a thickness comprised between approximately 15 cm and approximately30 cm, and being of PE having 5% boron filler.
 9. The system accordingto claim 1, wherein the deflection device is configured to emit amagnetic field having a value between 1 and 2 Tesla (T).
 10. The systemaccording to claim 1, wherein the deflection device comprises at leastone electromagnetic quadrupole positioned on a path of the irradiationbeam.
 11. The system according to claim 1, wherein the deflection deviceis composed of one or both of copper and iron.
 12. The system accordingto claim 1, wherein the at least two ports comprise at least three portsdisposed in a same plane.
 13. The system according to claim 12, whereinthe plane in which the ports are disposed is a horizontal plane.
 14. Thesystem according to claim 1, wherein the target holder mountingcomprises at least three ports disposed in a volume differently frombeing disposed in a same plane.
 15. The system according to claim 1,further comprising: a position adjusting device configured to adjust theposition of the irradiation beam; and a focus adjusting deviceconfigured to adjust the focus of the irradiation beam, wherein theposition adjusting device and the focus adjusting device are positionedupstream of the deflection device.
 16. The system according to claim 15,wherein the deflection device differs from the position adjustingdevice.
 17. The system according to claim 15, wherein the positionadjusting device and the focus adjusting device are positioned outsidethe radiation protection enclosure.
 18. The system according to claim15, wherein the position adjusting device and the focus adjusting deviceare conjointly formed by a pair of electromagnetic quadrupoles.
 19. Thesystem according to claim 15, further comprising an automatic modulecomprising a control module and a command unit, the control unit beingconfigured to integrate information and measurements concerning theposition and the focus of the irradiation beam and to send instructionsto the command unit, the command unit being configured to actuate one ormore of the position adjusting device, the focus adjusting device, andthe deflection device to optimize an interaction between the irradiationbeam and the target to irradiate.